It is well known in the art that a simple planetary gear assembly has an outer ring gear, a sun gear, planet gears intermeshing with the sun and outer ring gears, and a carrier for revolvably supporting the planet gears. In such arrangements, only a predetermined number of standard planet gears can be equally spaced between certain sizes of outer ring and sun gears. The predetermined number is determined by the space index. The sum of the number of teeth on the outer ring (“R”) and the number of teeth on the sun gear (“S”) is the space index. According to general principles of planetary gear design, the number of planet gears that may be used should be a whole number factor of the space index. Otherwise, equally spacing the planet gears around the circumference of the sun gear would not be possible. If the number of planet gears disposed around the sun gear is not a whole number factor of the space index, the planet gears cannot be equally spaced about the circumference of the sun gear. Unequally spaced planets cause problems such as, for example, uneven loading.
In addition, planetary gear assembly designs generally follow the tooth number correlation formula, namely that the number of teeth on the planet gear should equal the difference between the number of teeth on the outer ring gear and the number of teeth on the sun gear, divided by two (i.e., No. of Planet Teeth=(R−S)/2). This can result in frequent tooth reconnection and can restrict the number of planet gears that can be equally spaced about the circumference of a sun gear.
Some apparatus and methods have been developed to equally space planet gears around the circumference of a sun gear although the number of planet gears disposed around the circumference of the sun gear is not a whole number factor of the space index. One such method is described in U.S. Pat. No. 3,116,651 (the “'651 patent”) issued to Hardy. The '651 patent describes a method for equally spacing planet gears around the circumference of a sun gear using planet gears with different numbers of teeth. The method further alters the tooth shape of the planet gears to ensure meshing.
Although the method of the '651 patent may provide a mechanism to equally space planet gears around the circumference of a sun gear even though the number of planet gears may not be a whole number factor of the space index, altering the tooth profiles of planets to ensure meshing compromises gear kinematics.
The invention, as represented by the disclosed embodiments, for example, is directed to overcoming one or more of the problems set forth above.